A person is standing on a sheet of ice so slippery that friction may be ignored. This individual fires a gun parallel to the ground. When a standard cartridge is used , a 17-g bullet is shot forward with a speed of 270 m/s, and the person recoils with a speed of vc. When a blank cartridge is used , a mass of 0.2g is shot forward with a speed of 60 m/s , and the recoil speed is vb. Find the ratio vb/vc.
2007-10-12 16:50:50 · 2 answers · asked by Anonymous in Science & Mathematics ➔ Physics
Andrew Z's answer is right, but unnecessarily complicated. Use the principle of conservation of momentum:
Let "M" be the gun's mass.
Case 1:
momentum of bullet = recoil momentum of gun
(17g)(270m/s) = M(vc)
Case 2:
momentum of blank cartridge = recoil momentum of gun
(0.2g)(60m/s) = M(vb)
Now to find vb/vc, notice that vb/vc is the same as [M(vb)] ⁄ [M(vc)]:
vb/vc = [M(vb)] ⁄ [M(vc)] = [(17g)(270m/s)] ⁄ [(0.2g)(60m/s)]
2007-10-12 17:48:33 · answer #1 · answered by RickB 7 · 0⤊ 0⤋
Here's the trick to figuring it out: Newton's action reaction law. An equal amount of force is going to act on the person as on the bullett. Figure out the force, and apply it as a ratio between the masses.
2007-10-13 00:01:33 · answer #2 · answered by Andrew Z 2 · 0⤊ 0⤋